To investigate the effect of lean body mass on the survival and prognosis of patients with hematological malignancies including leukemia lymphoma and multiple myeloma . Method 312 patients with hematological malignancies from January 2014 to February 2020 were enrolled in a single center. Subjective global assessment PG- SGA and body composition analysis BiodynamicsBIA450 were performed within 48 hours after admission. Male lean body mass P15 = 35. 7 kg female lean body mass P15 = 28. 7 kg for grouping males ≤35. 7 kg were included in low lean body mass reorganization females ≤28. 7 kg were included in low lean body mass reorganization. The basic conditions of the research subjects were compared and the biochemical indicators anthropometric indicators and survival conditions were compared between the two groups. Result Among 312 patients 262 patients with normal lean body weight were classified as normal lean body group and other 50 patients with low lean body weight were classified as low lean body group. In leukemia patients the albumin and lymphocyte of normal lean body mass group were significantly higher than those of low body mass group P<0. 05 . In addition in patients with multiple myeloma and malignant lymphoma there was a statistical correlation between body measurements BMI MAC TSF MAMC and CC and lean body mass group P<0. 05 . Kaplan-Meier survival curve and Log-rank test showed that the survival rate of low lean body group was lower than that of normal lean body group P<0. 001 Cox regression analysis showed that low lean weight was a risk factor for hematological malignancies total HR= 2. 361 95%CI = 1. 455-3. 834 malignant lymphoma HR = 2. 331 95% CI = 1. 213-4. 477 multiple myeloma HR = 6. 348 95%CI = 1. 579-25. 520 . Conclusion Lean body mass in patients with hematological malignancies significantly affects the prognosis and survival of patients. It is recommended to strengthen individualized nutritional intervention to improve low lean body mass and improve the prognosis of patients.